In the field of biochemistry, gene technology and medicine, minute sample quantities are obtained, detected, analysed, handled or processed. Often the tasks consist of transferring the samples which are dissolved or suspended in a liquid, between macroscopic receptacles such as e.g. micro titre plates (μl volumes) and miniaturised carriers such as e.g. membranes, filters MALDI-MS targets, silicon wafers or nano titre plates (nl volumes). Tools known for transferring minimum substance quantities (lower limit approx. 1/10 nl) are so-called pin tools where the samples to be transferred adhere to needle points, or micropipettes or microdispensers where, analogous to inkjet printing technology applications, minute droplets with the incorporated sample are placed on the respective target substrate. Transfer at the interface between macroscopic receptacles and miniaturised carriers is generally associated with the problem that as a result of using part of the sample quantity present in the macroscopic receptacle, after transfer to the miniaturised carrier the quantity of substance present is insufficient to undertake a reliable analysis or treatment step. For this reason there is an interest in concentrating, collecting and/or purifying substance quantities in small volumes (μl range).
In the detection of substances of interest, mass-spectrometry processes nowadays achieve detection sensitivities in the attomol to lower femtomol region. Such sensitivity can effectively be used in practice only if the analyte is present in as pure a form as possible, at a volume comprising only a few nanolitres. For this purpose too, there is an interest in purifying or enriching substance samples.
From chemical and biochemical analysis it is generally known for sample enrichment to introduce solid phases in the respective solution or suspension, to which solid phases the desired molecules can temporarily be bound. With suitable magnetic materials properties, the solid phases can be manipulated under the influence of magnetic field forces (magnetic purification).
From U.S. Pat. No. 5,186,827, a magnetic separation device for separating magnetic particles from a non-magnetic test medium is known. The magnetic particles are small particles to whose surfaces the substances of interest are bound, or for example biological cells into which magnetic substances have been incorporated. With the use of a multitude of magnets, a magnetic field gradient is established in the test medium such that the magnetic particles are moved to the walls of the vessel where they are collected. The magnetic separation device known from U.S. Pat. No. 5,186,872 has the following disadvantages.
The design of the separation device is complex. To form the field gradients, at least four magnets are required which have to be arranged in a predetermined way and which require the use of particular receptacles for the test medium. In particular when electromagnets are used, the conventional separation device, which has been designed for characteristic receptacle dimensions in the cm region, does not allow miniaturisation. This precludes its use on the above-mentioned interface between macroscopic receptacles and miniature carriers with the tools used. Moreover, the conventional separation device is limited to separation only. There is no provision for loading magnetic particles with the substances of interest in the separation device.
From U.S. Pat. No. 5,498,550 a sample collector is known in which complexes of protein samples and magnetically marked antibodies are manipulated in a reactor under the influence of an external magnetic field. However, this sample collector is not suitable for handling substance quantities with volumes in the nl to μl range. A further disadvantage is that the respective antigen-antibody reaction for complex formation is limited to particular substances. Furthermore, a system for controlling magnetic particles in pipetting arrangements is known from WO 97/44671 and JP 08/062,224 (in: Patent Abstracts of Japan, 1996). The magnetic particles are suspended in a pipette-shaped cell; they can be pulled to the rim of the cell using an external permanent magnet. When the permanent magnet is removed, the particles are released and can therefore sink to the lower end of the cell which is open. But this system too is limited to manipulation of larger sample volumes in the ml range. Furthermore there is an advantage in that particle control only comprises binding or release, but not targeted movement of the particles in the cell. A magnetic separation device is described in WO 96/09550 (or U.S. Pat. No. 5,567,326) in which magnetisable particles are extracted from a non-magnetic test medium. The test medium is accommodated in a cell arrangement in which each cell is adapted for immersing a pin-shaped permanent magnet. This technology is associated with the disadvantage that the cells do not allow any dispersing of the test medium and that consequently the test medium is difficult to handle.
Further systems for manipulating magnetic or magnetisable particles are known from WO 86/06493, WO 89/01161, U.S. Pat. No. 5,147,529 and U.S. Pat. No. 3,985,649. However, none of these systems allow delivery of media in the same way as a dispenser. However, this dispensing function is of decisive importance in particular in the context of the tasks in biochemistry, gene technology and medicine mentioned above.
From WO 97/31105 a method for treating biopolymers, micro-organisms or materials with several types of magnetic particles is known. The materials to be treated are placed in a reservoir with the magnetic particles and bound to their surfaces. With a pipette, samples are taken from the supply vessel. Under the influence of a magnetic field, magnetic particles with bound materials can be held fast in the inside of the pipette. From WO 97/44134, a droplet shot device is known with which microscopic liquid droplets can be transferred to substrates.
At present, no purification or enrichment technology is known which can be used for processing (e.g. handling, collecting, purifying or similar) extremely small substance quantities (down to the nl range and below).
It is accordingly an object of the invention to provide a method for processing extremely small substance quantities which in particular is compatible with the use of traditional tools for handling samples in the nl-range and which has the widest possible scope of application. The method is to be easy to integrate into the conventional methods for handling samples, for detecting samples and for processing samples from biochemistry, gene technology and medicine. It is also the object of the invention to provide a device for implementing such a method.